1. Technical Field
The invention relates to shaft seals of the type used for sealing the gap between a housing and a rotary shaft, and more particularly to the construction and mounting of such seals to accommodate axial misalignment of the shaft and housing.
2. Related Prior Art
Compressors of the type used in air conditioning systems and the like include a rotatable shaft journaled within a compressor housing and carrying a working part such as a swash plate operative to compress a fluid refrigerant. The shaft extends through an opening or bore in the compressor housing and is rotated by a motor to drive the swash plate. A radial gap exists between the shaft and the housing bore which is closed by a shaft seal.
A typical shaft seal construction used in such compressor applications is shown diagrametically in FIG. 1. This seal has a metal carrier about the outer diameter of which is molded a rigid rubber mounting collar or sleeve sized in relation to the housing opening in which it is mounted to provide a press-fitted connection therebetween. In this way, the seal is caused to be aligned coaxially with the center axis of the housing bore and cannot move out of such alignment. The carrier also mounts an inner annular seal member having one or more lips encircling and dynamically sealing about an outer running surface of the shaft.
Optimum performance of the dynamic inner seal requires that the axis of the shaft be coaxially aligned with the axis of the seal so that the seal lips are uniformally loaded about their circumference. To achieve such coaxial alignment between the shaft and seal in the traditional seal system of FIG. 1, it is critical that the axis of the shaft be precisely aligned with the axis of the bore since the press-fit seal shares the same fixed axis as the bore. However, it is not uncommon for there to be some degree of axial misalignment between the shaft and bore due to inherent manufacturing tolerances, which must be borne by the seal. In the FIG. 1 arrangement, it will be appreciated that upon press fitting the seal into the bore of a housing, any misalignment of the shaft with respect to the bore will result in corresponding misalignment between the shaft and seal, making such seal press-fitted prone to early wear.
Accordingly, what is needed in the industry is a seal system that can accommodate variation in the axial relationship between the shaft and housing bore without impairing the sealing performance of the seal.
According to the invention, a self-centering shaft seal system is provided comprising a housing formed with a bore having a generally cylindrical wall of predetermined diameter disposed about a bore axis and an annular sealing shoulder disposed transverse to the axis. A shaft is supported for rotation within the bore having a generally cylindrical running surface disposed about a shaft axis. A seal assembly is disposed about the shaft and includes a metal carrier on which at least one radially acting shaft seal element is mounted about a longitudinal seal axis in dynamic sealing relation to the outer running surface of the shaft. The seal assembly also includes a face seal disposed axially between the carrier and the transverse sealing shoulder of the housing. According to a characterizing feature of the invention, the seal assembly is radially undersized in relation to the bore wall such that a radial clearance gap exists between the carrier and the bore wall free of any radial obstructions that would prevent radial movement of the seal assembly relative to the bore wall so as to enable the shaft seal element to support and center the seal assembly coaxially on the shaft, including when the shaft axis is misaligned with the bore axis, through a corresponding radial displacement of the seal assembly within the bore of the housing. Once aligned and mounted, the shaft seal element remains centered coaxially with the shaft during operation for optimum performance of the shaft seal element.
Accordingly, one advantage of the present invention is that the present seal system provides a shaft seal of a construction and size relative to the bore of the housing to enable the seal to center itself properly on the shaft whether or not the shaft is properly aligned with respect to the bore. Upon installation of the seal assembly within the bore about the shaft, the seal assembly will naturally seek its uniformally loaded condition, shifting the carrier if necessary radially within the bore to achieve coaxial alignment with respect to the shaft, even though the seal assembly may end up misaligned with respect to the bore. Such misalignment between the seal and housing is possible by provision of the designed-in clearance gap between the seal assembly and bore wall. Once centered, the seal assembly can be axially loaded by a snap ring or the like to urge the face seal into static sealing engagement with the transverse sealing shoulder of the housing to maintain the centered position of the seal assembly relative to the shaft and to prevent leakage of fluid past the carrier.
A method is also provided of sealing a rotatable shaft supported for rotation within a bore of a housing. The method involves forming the bore to include a bore wall of predetermined inner diameter disposed about a bore axis and a sealing shoulder disposed transverse to the housing axis. A seal assembly is provided having an outer diameter that is relatively undersized in relation to the inner diameter of the bore such that a carrier of the seal assembly is spaced from the bore wall to define a radial clearance gap therebetween. The carrier is provided with a shaft seal disposed about a seal axis and a face seal disposed transverse to the seal axis. The seal assembly is slid into position on the shaft within the bore to bring the face seal into position between the carrier and the transverse sealing shoulder of the bore. The shaft seal is allowed to center itself coaxially on the shaft independently of any misalignment between the shaft axis and the bore axis through corresponding radial displacement of the seal assembly within the bore of the housing.
The method shares the same advantages discussed above in connection with the seal system of the invention.